The invention relates to a non-invasive compressive device for use with ultrasound, and more particularly to a pressure tourniquet having a window that is transparent to ultrasound and a method of use.
The venous system contains a plurality of valves for directing blood flow to the heart. The venous system of the lower limb consists essentially of the superficial venous system and the deep venous system with perforating veins connecting the two systems. The superficial system includes the great saphenous vein and the small saphenous vein. The deep venous system includes the anterior and posterior tibial veins which unite to form the popliteal vein which in turn becomes the femoral vein when joined by the small saphenous vein.
Venous valves are usually bicuspid valves, with each cusp forming a sack or reservoir for blood which, under pressure, forces the free edges of the cusps together to prevent retrograde flow of the blood and allow only antegrade flow to the deep veins and heart. When an incompetent valve attempts to close in response to a pressure gradient across the valve, the cusps do not seal properly and retrograde flow of blood occurs. Venous insufficiency is a chronic disease involving the incompetence of venous valves.
Chronic venous insufficiency is a problem caused by hydrodynamic forces acting on the lowest part of the body, the legs, ankles and feet. As the veins dilate due to increased pressure, the valves in the veins become less able to withstand the weight of the blood above them. The weight of the blood causes the veins to dilate further and the valves in the veins to fail. Localized incompetence of a venous valve allows reflux of blood from the deep venous system to the superficial venous system. Reflux may be expressed as the peak reverse velocity of blood as a function of vein diameter. Patients with phlebitis may have damaged vein valve leaflets. A non-invasive manner of assessing the structural integrity or competency of venous valves is needed.
Patients who develop chronic venous insufficiency of the lower extremities frequently develop complications of this disease, including skin discoloration, varicose veins, and ulcerations. These patients may develop blood clots in their legs which can travel to their lungs, resulting in a pulmonary embolism. These complications develop over time, with increasingly severe damage to the veins and the valves within the veins.
The morphology of venous disease can be determined by the descending venography. This study requires that patients have an intravenous catheter placed in their groin and have multiple injections of radiographic contrast material injected while having multiple x-rays taken of the legs. The patient is held in various positions and tilted to allow the contrast material to flow into the veins. However, the contrast material has inherent medical risks of allergic or anaphylactic reactions. In addition, needles and canulas are placed into the patient at multiple sites for contrast injection.
Continuous-wave (CW) doppler is a commonly used method of evaluating venous reflux. This method, however, cannot determine precisely which veins in the path of the sound beam are being detected, thereby creating uncertainty about the vein being examined at the treatment site. Duplex ultrasound scanning can allow precise localization of the area being tested, as well as detect changes in flow direction. Both imaging, for localizing a vein, and Doppler processing, to detect flow and flow direction, are provided. When evaluating venous valve incompetence, the valves under evaluation should be closed. To elicit reflux for Doppler or ultrasound evaluation, the methods of the Valsalva maneuver, and compression of the limb containing the veins can be used with the patient in the supine and upright positions. Standardized compression can be achieved with pneumatic cuffs.
The Valsalva maneuver can be used by the patient to increase abdominal pressure to induce reflux in the lower limb. The Valsalva maneuver involves a forced expiratory effort against an airway, the strain of this effort causing high intrathoracic pressure which impedes venous return. However, the Valsalva maneuver has a variable effect on femoral venous diameter and on distal deep venous pressure when the patient is in the supine position. The reflux produced can be of variable duration because of the variable anatomic presence of the ileofemoral valves. When an ultrasound transducer is distal to a functioning valve at this level, the Valsalva maneuver does not produce the necessary transvalvular pressure gradients for closure of the valve.
Reflux in veins can be decreased by external compression. Pneumatic compression devices have been used to obtain closure of a venous valve with physiologic transvalvular pressure gradients. A cuff placed around a leg is inflated and rapidly deflated to simulate muscle relaxation to elicit valve closure. The cuff is located distal to the ultrasound transducer. The distance between the release of distal compression and the transducer is small to facilitate locating the site of venous incompetence. The area of the limb which is compressed by the cuff cannot be evaluated by ultrasound, so such measurements are taken along areas adjacent the tourniquet. A water-filled cuff has been proposed to vary the applied pressure to a limb while allowing ultrasound imaging of the veins through the cuff. However, disadvantages to this approach exist. The water-filled cuff can be bulky, heavy, and may not present a uniform or consistent ultrasound medium. If the cuff is constructed of an inelastic material, the cuff may contain air bubbles or form an irregular contact surface for the ultrasound transducer depending on the amount of water filling the cuff. Water leaks can arise that interfere with the operation of the cuff.
After determining the sites of venous incompetence, treatments such as compressive stockings worn about the patient's limb are often used to treat the disorder. However, it may be required to use such compressive stockings on a daily basis which could result in major lifestyle changes for the patient. Indirect valvuloplasty is another procedure in which an inelastic polyester cuff is wrapped around the vein itself to reduce the diameter of the vein. However, such a surgical procedure can be laborious and highly invasive, which has its associated complications with risk to life and expense.
Hence, there is a need for a system and method that would allow for a non-invasive or minimally invasive assessment of the condition of the veins and to locate incompetent valves. There also exists a need for a system that can determine the amount of diameter reduction of the vein in order to improve coaptation of venous valves and venous function. Such a system and method should be capable of being used in conjunction with a treatment that would durably reduce the diameter of a dilated vein to restore venous function. The invention fulfills these needs and others.